Step 1: Remove the Studs and Exterior Wall

In this project, two windows are being installed, one over the other, during this whole house remodel.

With the interior wallboards torn off, remove all insulation from the stud cavities. Relocate any electrical boxes or wiring.

Determine the rough opening for the new windows and use a reciprocating saw and sledgehammer to remove all obstructing studs and exterior wall (Image 1). Adding a flush-cut adapter to the reciprocating saw makes it easier to cut where the studs attach to the exterior wall (Image 2).

Step 2: Create the Header

If necessary, add full-height "king" studs from top plate to bottom plate to frame the windows. After measuring for the header, add a short stud ("jack" stud or "trimmer") on the inside of the "king" studs to support the new header. Nail the jack stud directly to the king stud on both sides of the opening. Take your level and make sure that the jack studs are level and at the same height

To create the header, cut to length two LVL (laminated veneer lumber) beams and place them on top of the jack studs. The new header should sit flush to the ceiling rafters above it and flush to the inside surface of the studs. Secure the header beams in place with a framing nailer.

Step 3: Add a Mullion Between the Windows

Measure the outside dimensions of the window, and transfer those measurements to the opening. If necessary, add 2"x4"s to both sides to bring the opening to the correct width to receive the window.

Add a horizontal 2" x 4" (a so-called "transom") between the windows so you will have something to fasten the nailing flanges to. Support the bottom 2" x 4" with smaller blocks of 2" x 4"s.

Step 4: Apply Water-Resistant Barrier and Set Window

Apply the water-resistant barrier provided by the window manufacturer or supply your own house wrap to go around the window on the exterior sheathing.

Pull out the nailing fin of the window and set the window into the opening you've just constructed.

Step 5: Add Shims and Secure the Window

Check for level and plumb, and add shims as needed (Image 1).

Secure the window by nailing into the nailing fin (Image 2) all around the window. Check that the window opens and closes correctly.